Automatic air valves for duct systems which both prevent the discharge of contaminated air therefrom, and allow ambient air to enter the ducts when a negative pressure occurs therein (for example, upon the flushing of a water cabinet of a sanitation system) are well-known. Such automatic air valves have been disclosed in U.S. Pat. Nos. 3,923,081 issued to Persson and 4,232,706 issued to Ericson.
In the automatic valves of which I am aware, the valve members, which control the flow of air in and out of the duct, must be capable of freely moving in response to certain pressures and air movements. Accordingly, these valve members are quite sensitive, being readily subject to being blocked or knocked out of alignment. This blockage or misalignment may interfere with the proper operatio of the valve by, for example, preventing the valve member from being fully opened (unseated) or closed (seated). A major source of such blockage and interference are insects, small animals and other foreign objects, such as debris, which may enter the valve from the ambient enviorment and come into contact with the valve member therein.
To solve the problem of blockage or interference resulting from such foreign objects from the ambient environment, an automatic air valve was disclosed in U.S. Pat. No. 4,535,807 issued to Ericson. In this valve, a grill is disposed over the exterior end of the passageway through which the air passes into the conduit. This grill acts as a filter for preventing and protecting against the entry into the passageway of those foreign objects, thereby preventing them from coming into contact with, or otherwise interfering with, the proper operation of the valve member.
While such an arrangement is extremely useful for preventing the entry of foreign objects from the ambient environment, it offers no protection whatsoever from foreign objects, such as insects, reptiles, small animals or other matter which originate from within the duct system itself. In warmer climates, such as in certain southern portions of the United States, it is common for insects and reptiles (such as snakes) to inhabit such duct systems, especially when the ducts are part of a sanitation system. These foreign objects originating in the duct system can, despite the existence of the grills disclosed in Ericson' 807, still come in contact with, and/or otherwise interfere with the proper operation of the valve member (for example, by preventing the valve member from being fully opened and/or closed), and of the automatic air valve.
Complicating this problem is the fact that sometimes these valves must be interposed directly in the conduit flow line of the duct system. In such cases, the valve must be equipped so that the flow of fluids and/or solids through the conduits of the duct system is not obstructed.
Thus, it can be seen that there remains a need for an automatic air valve for ducts, and in particular for the ducts of a water system or a sanitation system, which provides a means by which foreign objects, such as insects, reptiles, small animals, etc., may be retained in the duct system, so that they are restrained from operatively interfering with the valve member. It can further be seen that there remains a need for such an automatic air valve which is equipped so that fluids and solids may pass therethrough unobstructed, thereby permitting the valve to be interposed directly within the conduit flow line of the duct system.